Replacing the Floor Area Ratio

See the more recent post: "Graduating from the Floor Area Ratio"

The floor area ratio FAR is a planning regulation that provides erratic architectural design leadership. A ratio of 2.0, for instance, means that the gross building area can be twice the land area. Height is left as on option to encourage a smaller building “footprint” and the inclusion of project open space, but the open space decision has been discretionary. It is often omitted as a result, and the building population joins the public burdened by excessive intensity on parking lots and crowded ribbons of sidewalk.

The problem begins with the concept of buildable land area BLA. When a floor area ratio FAR is multiplied by the total land area owned, the assumption is that all of the land is buildable. If it contains ponds, extreme topography, marshes, ravines, unstable soil, etc., the buildable land area BLA is less than the total land area GLA and the gross building area GBA permitted must be placed on this smaller land area. The result is increased intensity on a reduced buildable land area BLA that is not anticipated by the FAR of 2.0. I’ve discussed the site plan hierarchy of gross land area GLA, net land area NLA, buildable land area BLA, core land area CORE and project open space S in “Context, Capacity and Intensity”, so I’ll simply say that the FAR begins to provide erratic leadership and random results when it is not multiplied by the buildable land area BLA involved.

Architectural design leadership becomes more unreliable when the FAR fails to specify the project open space percentage S required. Tables 1 and 3 illustrate the intensity levels produced when project open space S varies and the gross building area GBA is a constant found by multiplying the buildable land area BLA by a given FAR value. Tables 2 and 4 illustrate the increased intensity produced with the same project open space S range and land area when the constant gross building area GBA is increased by multiplying the gross land area GLA by the same FAR value.

Tables 1 and 2 are based on the CG1L forecast model, which addresses non-residential land uses with grade parking around, but not under, the building. This design solution is generally found in suburbs. Tables 3 and 4 are based on the CNPL forecast model, which is based on the absence of a parking requirement. This design solution is generally found in central business districts that were initially formed before the automobile.

All tables are based on the same gross, net and buildable land areas GLA, NLA and BLA. They are also based on the same design specification values, except for the FAR value. Tables 1 and 2 are based on an FAR of 0.25. This ratio is multiplied by the buildable land area BLA in Table 1 and the gross land area GLA in Table 2 to find the gross building area GBA permitted. Tables 3 and 4 are based on an FAR of 6.0, which is multiplied by the buildable land area BLA in Table 3 and the gross land area GLA in Table 4 to find the gross building area GBA permitted.

Table 1 illustrates the issues common to all tables. Project open space options S from 10% to 90% are listed in the left hand column of the Planning Forecast Panel. The floor FLR column displays the building floors needed to achieve a fixed gross building area GBA objective when the project open space percentage S varies. The FAR value given is noted in the design specification template. The INT column shows that intensity INT declines as project open space S increases. The CXT column indicates that context design potential increases as intensity declines. (This equation has changed from that presented in my essay, “Taking the Pulse of Architecture”, to better define the relationship of context potential to intensity.) The mathematical results are expected, but the entire range of options has rarely, if ever, been forecast from design specification values for comprehensive intensity evaluation.

Table 1 illustrates the point. One FAR value can produce many different intensity INT and context CXT options when project open space S and other underlying design specification value decisions are discretionary. This is not leadership with an objective that can protect our source and quality of life.

If you look at Table 1 from a developer’s perspective for a moment the issue comes into focus. The 10% open space provision produces fewer floors, less capital investment and lower context improvement and maintenance cost. It also introduces the greatest intensity at street level. If you were a developer, would you elect to provide more project open space and less intensity at greater cost for the same gross building area -- if the open space protected the public welfare? The odds favor less project open space, and in the recent past the odds were also against light, air and ventilation as a basic human right.

It has taken legislation to protect the public health, safety and welfare; and I have interpreted “welfare” to mean its physical, social, psychological and economic quality of life. From this perspective, the work is not complete. Shelter will only protect a growing population’s quality and source of life when land use allocation and urban form avoid excessive intensity and sprawl.

Table 2 illustrates that the intensity problem is exacerbated when gross land area GLA is substituted for buildable land area BLA in the equation GBA = FAR * BLA, even when all other design specification values remain constant. The obvious difference between Tables 1 and 2 is the increase in potential gross building area GBA, even though the FAR remains constant at 0.25. Less obvious, but very real, is the increase in height FLR and intensity INT on the buildable land area BLA when a larger gross building area GBA is introduced.

Table 1 illustrates the impact of increasing project open space S on building height FLR and intensity INT when the gross building area objective remains constant. Table 2 illustrates the same characteristics for a different gross building area GBA objective. The underlying point in both tables is that intensity INT can be excessive when project open space choice is left to individual discretion. We recognize the problem when we see it, but haven’t spent the time to define the condition requiring correction. This knowledge will become critical when we recognize that sprawl is a universal threat to survival, and that containment will involve a thorough grasp of intensity options and implications within the sustainable geographic limits we define.

Fortunately, intensity regulation involves a simple specification, but its use will be premature until knowledge leads to justification. The simplest form defines the number of floors permitted (f) and the project open space percentage required (S) when sky-plane requirements are not included. All ensuing architectural detail involves final plans, systems, form and appearance for the mass defined by this simple statistic. The combination of intensity prediction INT, evaluation, correlation, and regulation f.S can protect a population’s physical, social, psychological and economic welfare. The result will be a quality of life illustrated by urban form within sustainable geographic limits. At this time, however, we have predictive ability without implication knowledge; but the ability to predict with design specification values gives us the ability to measure these values at existing locations. Evaluating these measurements will give us the knowledge we need to convert predictions to protection of the public health, safety and welfare.

Tables 1 and 2 involved the CG1 design premise, but the FAR is often associated with more intense urban development. In these cases, parking may not be a requirement. Tables 3 and 4 were created to illustrate these conditions based on a FAR of 6.0. The design specification template is the same as that in Tables 1 and 2, but the (s) and (a) values related to parking are 0.0.

Table 3 finds the gross building area GBA permitted by multiplying the buildable land area BLA by the FAR value given. It again reveals the dramatic difference in gross building area GBA, building floors FLR, and intensity INT that results when project open space S varies while the FAR value remains constant.

Table 4 illustrates the same lesson, but is based on multiplying the gross land area GLA by the FAR to find the gross building area GBA permitted. Tables 3 and 4 are like Tables 1 and 2. Each table illustrates the increase in building height FLR and the declining intensity INT produced by increasing percentages of project open space S. Comparing Tables 3 and 4 illustrates the increased intensity placed on the buildable land area BLA when the maximum permitted gross building area GBA is a function of FAR * GLA rather than FAR * BLA.

The values in Tables 3 and 4 are greater than Tables 1 and 2 because parking is not required. All four tables illustrate, however, that the FAR ratio will produce random results without further leadership definition. The need for this definition is becoming more apparent as we recognize that growing populations must be protected from excessive intensity and sheltered within sustainable limits to protect their quality and source of life.

The statistics in Tables 1 – 4 document professional intuition with mathematical prediction. This makes it possible to elevate the city design of urban form from talent to leadership with quantifiable forecasting and evaluation. This will lead to credible public explanations that will not interfere with final architectural design solutions. It will provide the preliminary leadership needed. The policy is to protect the source and quality of life for growing populations. One goal is shelter within sustainable geographic limits. One tactic is to weave these shelter solutions together with open space and serve them with symbiotic movement and life support systems. This is the next level of awareness and adaptation will be required to protect a gift that does not compromise with ignorance.

Postscript

The intensity column INT in Tables 1 – 4 states that intensity is equal to FAR / S. This may be confusing to some readers who have seen it expressed as Ix = GBA / S * BLA in previous essays. The two are equal statements when FAR = GBA / BLA. This can be explained with the following derivation.

Ix = GBA / (S * BLA)

FAR = GBA / BLA

GBA = FAR * BLA

Ix = FAR * BLA / (S * BLA)

Therefore, Ix = FAR / S

This essay has pointed out that the equation GBA = FAR * GLA can produce an inflated result when gross land area GLA does not equal buildable land area BLA. The larger gross building area GBA result must still be placed on the smaller buildable land area BLA, which produces greater intensity INT and a greater actual FAR value for the land occupied.

(See also, "Replacing Density")